Mix the cauliflower and the prawns in any proportion that suits your taste or budget.
Quarter and peel the avocado, then slice each quarter carefully, and as thinly as you can, into a fan shape.
Cover all ingredients with a little lemon juice and arrange on four small plates of a contrasting colour.
Mix the soured cream and horseradish to taste and spoon on to each dish.
Scatter with finely grated lemon rind and serve well chilled.